# Proposed AD 99-SW-11-AD: McDonnell Douglas Helicopter Systems (MDHS) Model 369E, 369FF, 500N, and 600N Helicopters

- Type: Proposed airworthiness directive (not in force)
- Status: Became AD 99-08-07
- Action: Final rule; request for comments.
- Published: April 6, 1999, 64 FR 16656
- Became: [AD 99-08-07](https://openairdocs.org/ad/99-08-07)
- Docket: 99-SW-11-AD
- FR document: 99-8408
- Official PDF: https://openairdocs.org/files/sha256/2e/7b/2e7ba10b013832d927d0f6106f013646b8e2730033c0cb48f15eae07111bd336 (from https://www.govinfo.gov/content/pkg/FR-1999-04-06/pdf/99-8408.pdf)
- Federal Register: https://www.federalregister.gov/documents/1999/04/06/99-8408/airworthiness-directives-mcdonnell-douglas-helicopter-systems-mdhs-model-369e-369ff-500n-and-600n
- Page: https://openairdocs.org/proposed/99-SW-11-AD

## Summary

This amendment supersedes an existing priority letter airworthiness directive (AD) 98-17-14, applicable to MDHS Model 369E, 369FF, 500N, and 600N helicopters, that currently requires, within the next 14 calendar days, inspecting each relay receptacle contact socket for correct size of the contact socket holes and replacing incorrectly- sized contact sockets with airworthy contact sockets. This amendment requires the same inspections and replacements as the existing priority letter AD, but changes the serial numbers affected for the MDHS Model 500N and 600N helicopters and changes a part number that was incorrectly referenced in the existing AD. This amendment is prompted by three incidences in which a MDHS Model 600 helicopter's Engine Control Unit (ECU) Fail light illuminated, even though the ECU continued to automatically control the engine. The cause of the ECU malfunction indication was determined to be contact sockets that did not properly fit the corresponding pins of the affected relay. Improperly sized contact sockets could create multiple unsafe conditions. These conditions, if not corrected, could result in the loss of various engine control or warning systems including the undetected loss of the auto-reignition function after an engine flameout, failure of an engine to reignite, and a subsequent forced landing and the inability to immediately detect an engine-out condition or to properly govern main rotor speed following loss of the Full Authority Digital Engine Control (FADEC), and subsequent loss of control of the helicopter.

## Notices in this docket

- Apr 6, 1999: Final rule; request for comments. (first notice), FR document 99-8408 (https://www.federalregister.gov/documents/1999/04/06/99-8408/airworthiness-directives-mcdonnell-douglas-helicopter-systems-mdhs-model-369e-369ff-500n-and-600n)

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